This invention relates to a hull for shipping with a mono-three-catamaran architecture.
The total resistance to forward motion of a boat is basically the sum of the skin friction (that is obtained by integrating the tangential stress over all the hull surface in the direction of the motion), the viscous drag (that is connected to the energy dissipated owing to the viscous effects) and the residual resistance. The residual resistance includes to a great extent the wave resistance, that is connected to the energy dissipated by the hull in making gravitational waves.
A hull moving forward generates a global wave formation, that is constituted in turn by two distinct but interacting wave systems: a diverging wave system and a transverse wave system. The global wave formation is contained inside two lines, that are called boundary lines of the diverging wave system. Each boundary line forms an angle of 19.5 degrees with the longitudinal symmetry plane of the hull. The crest lines of the transverse waves are perpendicular to the direction of the hull motion near the hull and turn backward as the transverse waves approach the diverging waves until they join the same diverging wave system. In front of the bow of the ship there is a high pressure area that generates a prominent wave front as a part of the transverse and diverging wave system. Further wave systems form near the bow and stern sides of the hull.
A resulting wave system may be often considered as formed by four wave systems:
a bow wave system owing to the high pressure area that forms near the bow during the forward motion of the hull;
a wave system forward from the bow side portion owing to a low pressure area that forms near such a side portion;
a wave system that forms along the stern side portion owing to a low pressure area existing in such a part of hull;
a stern wave system owing to a high pressure area that forms in the stern area.
It is very difficult to foresee the exact position of the crest of both the bow wave and stern systems. It is likewise difficult to foresee the position of the troughs of the wave systems formed in the bow and stern side portions of the hull owing to high pressure peaks that are generated near said bow and stern side portions.
Said four wave systems that form the global wave system can interfere with each other in a more or less favorable manner for the resistance to forward motion of the hull. However, since the wave resistance contributes to the total resistance to a great extent, one should act just on the wave resistance by taking measures intended to reduce said wave resistance so that the propulsive power installed on a boat may be decreased, with the speed reached by the boat being the same.
In the last years the designers have had as a goal to reduce as much as possible the wave formation generated by the hull moving forward.
On the other hand, there are designs that improve the conditions of resistance to forward motion by utilizing the bow wave formations, holding in the same in the bottom of the hull and creating a more prominent resulting stern wave system. Among others, U.S. Pat. No. 5,402,743 issued on Apr. 4, 1995 to Holderman and entitled xe2x80x9cDeep Chine Hull Designxe2x80x9d, discloses a hull with a bottom structure forming two longitudinal channels which extend fore and aft along all the hull. In the above patent, the bow wave, being assisted in its rotatory motion and controlled in a certain measure, deviates into these channels. The bow wave is controlled through the conformation of said channels according to a Venturi tube. The inventor of the above patent makes it a condition, among the other things, that air in the bow of the hull is thrown out before being included inside the same channels. Further, this condition sets limits on the shape of the hull that must have curved sides, i.e. the hull is tapered in its cross sections toward the bow and toward the stern, and accomplishes a Venturi tube structure along all its length through a pair of inverted channels that border a continuous keel fore and aft.
This invention is close to the above patent only in the insight of diverting under the hull the bow wave formed in the forward motion.
However, differently from the above patent, an object of this invention is a hull, in which a portion of the energy spent to form the bow wave system is used to increase a hydrodynamic sustentation of the hull.
Another object of this invention is a hull in which the energy dissipated in both friction and viscous phenomena is reduced.
Furthermore, an object of this invention is a hull in which a resulting stern wave formation and then a dissipation energy connected therewith is limited.
Yet another object of this invention is a hull having a stability of shape whereby the hull goes steadily to a balance position whatever might be the speed of the shipping and, within limits, the conditions of the sea.
A further object of this invention is a hull having a length less than that of other hulls of shipping with equal carrying capacity.
For these purposes, the present invention provides a deep chine hull for shipping with a mono-three-catamaran architecture comprising:
a bow point connected to hull sides lying in vertical parallel planes symmetrically opposed to a center line that ends at a stern;
a pair of chines disposed laterally to the center line, each chine defining a lower edge of said hull sides, that begins at a desired cross section plane near the bow point under a waterline and thereafter defines a longitudinal line extending continually aftward to said stern;
a keel, beginning near the bow point and extending along the center line on the underside of the hull aftward for a length less than the distance between the bow point and the midship section;
a bottom extending laterally between said chines, and between every chine and said keel where the keel is present; a surface of the bottom having cross section planes at right angles with the center line forming convex bottom structures bridging a pair of inverted longitudinal bottom channels which extend laterally to said keel; said pair of channels merging aft from said keel with a single bottom channel having a profile with channel sides which are increasingly slanted in the stern cross sections and become parallel to the hull sides in the stern.
A hull so shaped according to the invention may be called a mono-three-catamaran.
Said bottom inverted structures have waterlines defining a bottom shaped as a diffuser with increased cross section areas, fore and aft, of said channel pair and of said single channel, in which the kinetic energy of the flow conveyed from bow is transformed into pressure energy.
Such a hull enables the energy dissipated in both friction and viscous phenomena to be reduced since air is conveyed under the hull inside the channels as above, not to create a continuous air layer and then use an over-craft effect, but to include air into water in order to carry on a boundary foamy layer. It is important to carry on a boundary foamy layer on the grounds of the following remarks:
i) if a continuous air layer is carried on, an optimal situation from the point of view of the reduction of the friction would be obtained; however, with the exception of a race-boat, the speed of the hull would not be high enough to compress the air layer to such an extent that the aerodynamic lift effect transferred to the hull is large;
ii) if the channel bottom surface is in direct contact with the water, there would be the best situation from a point of view of the hydrodynamic sustentation of a hull, but the worst from a point of view of the resistance to forward motion of a boat owing to an increase of the friction and viscous phenomena due to the widening of the wet surface;
iii) a foamy layer conciliates the need of decreasing as much as possible the friction resistance and the possibility of exploiting the hydrodynamic sustentation. Since the foam is constituted in general by very small spherical chambers containing air or gas (e.g. exhaust gas), the foam is rigid enough to allow a sufficient hydrodynamic sustentation to be transmitted with equal speed of the hull, against a reduced resistance to forward motion.
The foamy layer may be suitably obtained by conveying the bow waves, that are generated by both the keel and the chines, into the channels, and appropriately designing a propelling apparatus relating to both the choice and the arrangement thereof.
From the standpoint of the response of the hull according to the invention to the wave system generated when it is moving forward, the hull has a high pressure area in the bow in connection with the wave crest, a following low pressure area in connection with a wave trough and a subsequent low pressure area that would be formed aft from the keel beyond the point of maximum draft of the hull bottom. When the speed of the hull changes, the buoyancy center resulting from the pressure distribution above explained can fall fore or aft the center of gravity of the shipping. However, the longitudinal position of the hull may change only for a moment, since by changing the draft of the bow and the hull sides, the high pressure area and the following low pressure area would change as a consequence, resetting immediately the hydrodynamic balance. The greater or lower draft of the stern would change the cross sections of the effuser constituted by the ascending flat bottom aft from the keel, together with the internal sides of the chines, and would help to keep this balance. The flat bottom would function as a constant support for the hull. In conclusion, the hull according the invention xe2x80x9csails constantly on its wavexe2x80x9d, that is contained between its chines in the portion aft from the keel to the stern and guided in front by the stern and the keel.
Further, owing to the variation of pressure along the channels from the bow to aft of the keel, the water flow of the bow wave is subjected to a spiral right hand movement in the left channel and to a spiral left hand movement in the right channel, both helping the formation of air bubbles and increasing the foamy layer, with a reduction of the viscous friction.
One or two propulsors can change the pressure pattern under the hull, and then the position of the buoyancy center and the spiral movement above-mentioned.
The hull configured according to the present invention causes the bow wave formation so conveyed to give the hull back a portion of its energy in the form of an increase of the hydrodynamic sustentation. Further, a hull so configured allows, through both an appropriate selection of hull dimensions between its chines and a suitable arrangement of the propelling apparatus, the wave produced by the interaction of the wave systems generated in the motion of the boat to be controlled in its resulting height. This resulting height of the wave also depends on a dampening effect of said foamy layer.
Furthermore, the channel bottom surface, having convex cross sections as above, can be shaped so that the resultant of the thrust due to the hydrodynamic sustentation passes through the center of buoyancy approximately in order to not generate a trim variation both when the shipping is stationary or is navigating in a displacement way and when the shipping is navigating in a gliding way on its wave.